The regulations for cleaning and sterilizing re-usable surgical instruments make greater and greater demands which necessitate an ever more extensive ability to take apart re-usable surgical instruments. At the same time, instruments for micro-invasive interventions, in particular, are becoming smaller and smaller, in particular the cross sections and diameters of the shaft and the tool on the distal end of the shaft. Couplings, which are conventionally provided for releasable mechanical coupling between the tool and the shaft, however, are not able to be miniaturized in an arbitrary manner. Where a shaft diameter is 3.5 mm or less, new concepts for releasable mechanical coupling between the tool and shaft are necessary.